fdf -- the only way I see to change your player name would be to write down your mushers then select Leave League, then join the league again as fdf then select your mushers again.
I have also confirmed that you can delete a musher from your team and then add a different musher, right up to 10:00AM Alaska time on Saturday March 4th. The bib number selection (start order) or the dogs in the team or any other factor may cause you to reconsider your musher selections -- but only before 10:00AM Alaska time Saturday, March 4th.
Heidi also confirmed that you do not have to spend the entire $27,000. You must have exactly 7 teams, but you can spend up to $27,000 on those teams. Your total musher costs can add up to less than $27,000.